U.S. Pat. No. 5,092,151 and U.S. Pat. No. 5,199,293, a continuation of the '151 patent, each disclose particularly sheet working centers intended for bending, whereby separate means are used for accomplishing the approaching movement of the tool on one hand, and the actual working movement on the other hand. The means for accomplishing the approaching movement of the tool are constructed in a way that the approaching movement is relatively quick, and on the other hand, the means for accomplishing the actual working movement are constructed in a way that their movement is relatively slow in relation to the movement of the first means. On the other hand, the second means are constructed so that the force effect to be accomplished with them is considerably greater for the working of the sheet than the force effect accomplished by the movement of the first means which accomplish only a linear movement.
In said U.S. publications, the second means comprise a first gliding means fixed to a buffer arranged to be movable in the vertical direction, and a second gliding means arranged to move by actuators in the horizontal direction, wherein the working movement of the second means is accomplished by a wedging effect between the first and second gliding means. Between the wedge surfaces in the first and second gliding means, there are roll surfaces, by means of which the movement of the horizontally moving, wedge-like second gliding means is transmitted to the second gliding means as a vertical movement and thus to the working movement of the tool in the buffer bar.
The solution as set forth in the publications U.S. Pat No. 5,092,151 and U.S. Pat. No. 5,199,293 is disadvantageous in the respect that the approaching movement and the working movement are arranged to be effected by separate means and actuators using them. In consequence, firstly the construction using such a method is complex and expensive, because of the high investments on the required equipment; secondly, a complex control system is required for the successive approaching and working movements, which may easily cause operational risks.